1. Field of the Invention
The present invention relates to laminations and to methods for their making. In another aspect, the present invention relates to laminations having polymer coatings and to methods for their making. In still another aspect, the present invention relates to metal laminate structures formed from such laminations for electromagnetic devices such as motors, transformers and ballasts, having ultraviolet cured polymer coatings and to methods for their making.
2. Description of the Related Art
There are a number of applications such as electric power transformers, motors and electronics employing thin gauge sheets. Thin gauge electrical steel sheets or amorphous metal sheets for electrical applications reduce magnetically induced eddy currents by reducing the cross-sectional area through which those currents may flow. However, the core losses in electrical transformers used by electrical utility companies represent a significant loss of energy generated, even though electrical transformers are highly efficient.
It is well known that eddy current losses of electrical steel sheets can be decreased by reducing the sheet thickness and providing the sheets with an insulating film on the surface thereof. In the manufacture of cores for electric motors and transformers, the electrical steel sheets are continuously formed into blanks having the shape of a core, a predetermined number of the blanked sections are laminated together, and the edges of the resultant laminate core are fixed by welding. The insulating film is, therefore, required to exhibit not only an insulative property but also a number of other necessary properties, such as blanking capability, adhesion, lamination welding, heat resistance, and resistance against oil. It must also provide a high space factor.
A number of prior art patents disclose methods of forming the insulating film which attempt to satisfy these properties.
For example, one method discloses employing phosphate or chromate as components for forming an insulating coating. While the coating formed has good heat resistance and weldability, the blanking and adhesion properties are not satisfactory.
Japanese Examined Patent Publication No. 49-19078 aims to satisfy both the blanking property and the weldability requirements and proposes to form on an electrical steel sheet an insulating film having a surface roughness of H.sub.max of 2 mu or more by utilizing a dispersion of organic particles in the treating resin. However, this method suffers from a difficulty in achieving a good organic particle dispersion which affect the manufacture of the film and the adhesion of the film to the steel sheet.
Japanese Examined Patent Publication No. 55-21111 proposes a technique which addresses the problems of the particle dispersion by utilizing either phosphate or chromate in the treating liquid.
In an attempt to improve upon this technique, U.S. Pat. No. 4,681,377, issued Oct. 21, 1986 to Nakamura et al., suggests utilizing in the emulsion-resin solution a dispersion improver that is generally a nonionic-, ionic-, cationic-, or amphoteric- type surface-active agent.
U.S. Pat. No. 4,705,578, issued Nov. 10, 1987 discloses a method of constructing laminations of an amorphous alloy suitable for use in a magnetic core for static electrical inductive apparatus. The laminate formed will have an improved space factor and reduced core losses. The method generally consists of pressure annealing the metal laminations together without the use of polymer between the laminations. After the stress-relief anneal process step, the group of laminations may be edge bonded with a U.V. curable resin, as long as the resin is not allowed to penetrate the space between the laminations, to aid handling and to prevent the brittle laminations from shedding flakes.
U.S. Pat. No. 4,753,822, issued Jun. 28, 1988 to Van Mensvoort, teaches that the presence of the insulating layer on only a part of the surface is in many cases sufficient to suppress the occurrence of eddy currents. The insulating layer serves as a spacer between the laminations.
U.S. Pat. No. 5,018,267, issued May 28, 1991 to Schoen discloses a method for forming a laminate in which a thin layer of oil is applied to a facing of at least one of a plurality of adjacent sheets and a wax is applied along the longitudinal edges of a facing surface of at least one of the sheets. The sheets are combined into a laminate by being passed between a pair of rollers which apply sufficient pressure to remove excess oil from between the facing surfaces and to spread the wax thereby forming a continuous seal along the longitudinal edges of the laminate.
While the above references disclose methods of forming laminations and laminate structures that are suitable for use in applications such as electric power transformers, motors and electronics, they all suffer from one or more disadvantages. For example, the prior art references teach the use of nonoriented silicon steel having a silicon content in the 2 to 3 percent range instead of the more economical carbon or motor laminate steel having a much lower alloy content. Also in utilizing chemical bonding to hold laminates together the bonding agent is generally applied with a solvent that tends to cause shrinkage as it evaporates, or if vaporized under elevated temperature and pressure may cause blow holes. Such shrinkage, particularly for thin metal sheets, may strain or induce stress into the sheets. A further disadvantage of using chemical bonding is that an elevated temperature may be required to cure the bonding agent. Such an elevated temperature may diminish the effects of domain refinement treatments for electrical steel sheets.
It is therefore one object of the present invention to provide an improved method of making laminations.
It is therefore another object of the present invention to provide a method of making chemically bonded laminates that will not suffer from shrinkage problems nor require elevated temperatures for curing.
It is a further object of the present invention to provide for laminate structures having low interlaminar core loss.
It is still a further object of the present invention to provide for a method of making laminations from low alloy content steel.
It Is still a further object of the present invention to provide for an improved method of manufacturing making insulated electrical coils.